AppearanceA medium-sized fish that can reach a length of 60 centimeters . Small individuals are dark brown with hundreds of small, dark-edged iridescent blue spots. Larger specimens sometimes develop four to six lighter vertical bars on the back half of its body.
BehaviorRoi typically sit on a coral head, retreating when startled.
Red Sea males defend harems of 2-6 females in territories ranging up to .5 acres . Each female defends part of the territory from the other females. The male visits each female daily, raising his dorsal fin to signal his approach. The females emerges from hiding, erecting her own dorsal fin and changing to a lighter color. They swim together, rubbing flanks before he departs until the next day.
Territorial disputes may involve "color fights" in which two males positioning themselves at right angles to each other. They then darken their color and repeatedly switch their bars from dark to light. The loser becomes pale and retreats. If the color fight ends in a draw, the two males may attack each other.
ReproductionIn Micronesia, spawning usually occurs territorially at dusk. During courtship, both sexes darken except for a white keyhole-shaped patch at the center of the body.
FoodHunting, they lie on the bottom and surge forward, preferring juvenile surgeonfish and crustaceans. Alternatively they may hover motionless in the water column before attacking.
This grouper may follow and cooperate with another predator species, such as an octopus or eel or camouflage themselves in a school of surgeonfish. Multiple individuals may cooperate to harass an eel to get it to flush prey for them.
In the Red Sea, they hunt in the morning and evening.Analysis of stomach contents found that Roi diets consist of 97.7% fish and 2.3% crustaceans. Of the fish eaten, there were 27.1% ''Scaridae'' , 18.7% ''Acanthuridae'' , 17.6% Squirrelfish, 13.7% ''Monacanthidae'' , 9.3% ''Priacanthidae'' , 4.3% ''Chaetodontidae'' , 2.8% ''Aulostomidae'' , and 6.9% other consisting of 9 families. Roi are estimated to eat 0.8% of their body weight each day.
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